Determine the electric potential at the mid-point of the line joining two equal but opposite charges $q$ in terms of $q$, the coulomb constant and the charge separation $d$.

Four equal charges $5.0 \mathrm{\mu c}$ are placed at the vertices of a square side of $10 \mathrm{cm}$.

Calculate the value of the electric potential at the centre of the square. (use $K=9\times {10}^9$)

Four equal charges $5.0 \mathrm{\mu c}$ are placed at the vertices of a square side of $10 \mathrm{cm}$.

Determine the electric field at the centre of the square.

Four equal charges $5.0 \mathrm{\mu c}$ are placed at the vertices of a square side of $10 \mathrm{cm}$.

How do you reconcile your answer to $a$ part question and $b$part question with the fact that the electric field is the derivative of the electric potential $?$

Four charges are placed at the vertices of a square of side $5.00 \mathrm{cm}$, as shown in the diagram.

On a copy of the diagram, show the forces acting on $2.0 \mathrm{\mu C}$ charge. Find the magnitude and the direction of the net force on the $2.0 \mathrm{\mu C}$ charge. (use $K=9\times {10}^9$.)